By Nicole Montesano • Staff Writer • 

Treatment plant touts its accomplishments

Ossie Bladine/News-RegisterErik Grimstad performs a sludge check in one of the pools at the McMinnville sewage treatment plant.

In a memo to City Manager Kent Taylor, Gehring said that in addition to maximizing efficiency at the plant, the staff has worked with local industries to phase the flow of their waste products to keep them from overwhelming the system.

Water levels in the South Yamhill River drop dramatically in the summer, partly due to irrigation of surrounding farms and partly due to significantly reduced rain and snow melt runoff. As a result, restrictions on pollutant release are particularly stringent.

For that reason, Gehring said, “Starting in May each year, the staff begins to transition the wastewater plant to 'summer mode.' This involves increasing process tests, keeping a close eye on the river level, and making adjustments to the plant to efficiently lower the concentration of pollutants. This 'summer mode' lasts through Oct. 31."

This year, he said, “In August this year, 99.9 percent of ammonia and 99.4 percent of phosphorous were removed from the waste stream. The final concentration of ammonia was 0.026 milligrams per liter, which is equivalent to 3 grains of rice in a 150-pound bag.”

Ammonia and phosphorous are two of the “most complex pollutant parameters that must be removed from the wastewater. If too much of these pollutants are introduced into the river, algae will grow in excess, damaging aquatic life.”

The permit allows the plant to release 70 parts per billion of phosphorous, Gehring said, but staff was able to achieve 35 parts per billion.

“This facility is well run," Gehring said. "It's one of the nicest facilities in the Northwest. The folks here take a lot of ownership in the facility and the quality of the water we produce.”

The plant uses a combination process to remove phosphorous and ammonia, he said, first using bacteria to break them down, and then adding chemicals in order to "get the last little bit out.”

He said, “Our job is to make the perfect conditions to use bacteria to do what they do best,” by manipulating their environment in the treatment basins. “These things naturally happen in the environment, but we speed it up to make it better,” he said.

“The operations staff is the eyes and ears of the plant. Members make modifications to the process to optimize chemical addition, equipment speeds, and water levels based on results from process tests and observations. A computerized control system is used to help constantly monitor and regulate the system," he wrote.

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